RF pair with RSSI

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mrmrzamany

New Member
Hi i just found this RF https://www.sparkfun.com/products/10532

I have some questions ...
I'm working on a project using UAV, I want to place 4 of these RF (one in each side), because i want the UAV to go to the direction of the most received signal until it find the transmitter and locate it , say for example in one side the signal is 1 dB , and the other side (other receiver) read 10 dB, the UAV should go toward the 10 dB signal

1- first using the RF pair mentioned above, can i do that?
2- I didn't read if it has RSSI or not, does it has RSSI?
2- can I convert the output to TTL pulses or are they the same?
3- since I'll be using for transceiver, can i connect to them directional antenna to know from which direction the signal is coming, or I can do that using the transceiver only?
4- if you have other products that i can use let me know

thank you

Note: the system will work in indoor for example in a room that has an area of 5 meters x 4 meters
 
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M

mrmrzamany

New Member
hippy said:
The datasheet for the item linked to is at -

http://cdn.sparkfun.com/datasheets/Wireless/General/RWS-371-6_433.92MHz_ASK_RF_Receiver_Module_Data_Sheet.pdf

It does not appear to have any documented RSSI capability.

A Google search on "receiver with rssi" appears to bring up a number of RF receiver products and support chips which provide for RSSI.
Click to expand...
do you any idea about the directional antenna and how it can be used in order to know from which direction the signal is coming or if it can work with this RF and RSSI ?
 
hippy

hippy

Technical Support
Staff member
mrmrzamany said:
do you any idea about the directional antenna and how it can be used in order to know from which direction the signal is coming or if it can work with this RF and RSSI ?
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A directional antenna can be used with any RF receiver. As the directional antenna is pointed in different directions the strength of a signal received will vary; it will be highest when pointed towards the signal source. By pointing the antenna in different directions, noting the strength of the received signal from each, it should be possible to determine in which direction the signal is coming from.

This is similar to moving a satellite dish and monitoring signal strength to determine in which direction it should be pointing to best receive a satellite TV signal.

Did you investigate the suggestions given when you previously discussed this project -

http://www.picaxeforum.co.uk/showthread.php?29004-RF-emitter-receiver
http://www.picaxeforum.co.uk/showthread.php?29005-mimic-radiation-sensor-using-comunication-devices
 
M

mrmrzamany

New Member
hippy said:
A directional antenna can be used with any RF receiver. As the directional antenna is pointed in different directions the strength of a signal received will vary; it will be highest when pointed towards the signal source. By pointing the antenna in different directions, noting the strength of the received signal from each, it should be possible to determine in which direction the signal is coming from.

This is similar to moving a satellite dish and monitoring signal strength to determine in which direction it should be pointing to best receive a satellite TV signal.

Did you investigate the suggestions given when you previously discussed this project -

http://www.picaxeforum.co.uk/showthread.php?29004-RF-emitter-receiver
http://www.picaxeforum.co.uk/showthread.php?29005-mimic-radiation-sensor-using-comunication-devices
Click to expand...
Yes, thats why i reached this point to select what i want in this page http://winavr.scienceprog.com/example-avr-projects/running-tx433-and-rx433-rf-modules-with-avr-microcontrollers.html

there is a picture in the end of page "digital output" but I don't know if it has RSSI or not because I don't have the experience, can you help me with that?

if not can i just use this wireless transceiver and connect to it the directional antenna ?? https://www.sparkfun.com/products/12030

in a previous Thread you told that having TTL output is a minor issue, can you explain to me how..

I'm sorry if I'm asking too many questions but knowladge has no end, Ill share with you my project once I finish it :)
thank you
 
hippy

hippy

Technical Support
Staff member
mrmrzamany said:
I'm sorry if I'm asking too many questions but knowladge has no end
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Unfortunately it appears that you are lacking the fundamental knowledge which would be needed and a prerequisite for undertaking your project and this is not the best place to obtain such fundamental knowledge.

What you are attempting is quite an advanced project, best undertaken with a good understanding of basic principles and with a firm foundation and past experience to build on. It is not a project which would be easy to complete without those.

There are however some resources which could help you with your project, including this -

https://www.youtube.com/watch?v=X5IsB-BhoHk

"RSSI Project using PICAXE and Dorji 433MHz Transmitter and Reciever"
 
J

Jeremy Harris

Senior Member
mrmrzamany said:
Note: the system will work in indoor for example in a room that has an area of 5 meters x 4 meters
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There is your major problem. As soon as you place a radio transmitter in a room the transmission from it will be reflected from all the surfaces to some degree. If you put four transmitters in a room then the reflections will be such that I very much doubt that you will be able to consistently sense the signal strength from any of them, anywhere in the room. If you fit directional antennas the problem may be worse, as there will be even stronger reflections.

The only way that I think you could possibly get an RF signal strength based system to work in a room would be if the room was an RF anechoic chamber, where there would be virtually no surface reflections.

If you want to explore location within a closed room, then I'd suggest looking at using IR transmitters, with their beam restricted to match the cone angles of the corner of the room they are places in (to reduce reflections messing things up). It should be possible to use modulated IR and design and build transmitters and a receiver that would give signals that you could use for guidance.

Laser-guided bombs and IR sensing missiles used a very crude system with a quadrant sensor (four sensors arranged in a quadrant) with each controlling guidance fins. There was nothing proportional about them, they just worked by moving the fins to the limit of their travel when the signal in one quadrant was greater than that in any other quadrant, steering the missile/bomb back towards the centre. In practice the track was always a bit wobbly, with the missile/bomb over-correcting one way, then over-correcting another way, but it worked well enough to get the level of accuracy needed (laser-guided bombs that work like this are still around, as it's a simple and reliable system that just works).
 
hippy

hippy

Technical Support
Staff member
AIUI this is a 'drone locating an item in a room' challenge.

The ultimate application is to locate a radioactive source but the proof of concept will use RF rather than radiation.

There will be one RF transmitter attached to the item and four RF receivers on the drone, each with directional antenna. Received signal strength will be used to figure out where the item is.

That sounds simple enough, but so do many one line project specs written on the back of napkins.
 
M

mrmrzamany

New Member
hippy said:
AIUI this is a 'drone locating an item in a room' challenge.

The ultimate application is to locate a radioactive source but the proof of concept will use RF rather than radiation.

There will be one RF transmitter attached to the item and four RF receivers on the drone, each with directional antenna. Received signal strength will be used to figure out where the item is.

That sounds simple enough, but so do many one line project specs written on the back of napkins.
Click to expand...
Hello again,
thank you very much , I watched the video and understood the fundamentals

I have a question from where can I get the directional antenna ?? i searched the internet all of the antenna has coaxial wire how can i connect this wire to the small RF that i have, please if you guide me in this last thing :)
 
M

mrmrzamany

New Member
Jeremy Harris said:
There is your major problem. As soon as you place a radio transmitter in a room the transmission from it will be reflected from all the surfaces to some degree. If you put four transmitters in a room then the reflections will be such that I very much doubt that you will be able to consistently sense the signal strength from any of them, anywhere in the room. If you fit directional antennas the problem may be worse, as there will be even stronger reflections.

The only way that I think you could possibly get an RF signal strength based system to work in a room would be if the room was an RF anechoic chamber, where there would be virtually no surface reflections.

If you want to explore location within a closed room, then I'd suggest looking at using IR transmitters, with their beam restricted to match the cone angles of the corner of the room they are places in (to reduce reflections messing things up). It should be possible to use modulated IR and design and build transmitters and a receiver that would give signals that you could use for guidance.

Laser-guided bombs and IR sensing missiles used a very crude system with a quadrant sensor (four sensors arranged in a quadrant) with each controlling guidance fins. There was nothing proportional about them, they just worked by moving the fins to the limit of their travel when the signal in one quadrant was greater than that in any other quadrant, steering the missile/bomb back towards the centre. In practice the track was always a bit wobbly, with the missile/bomb over-correcting one way, then over-correcting another way, but it worked well enough to get the level of accuracy needed (laser-guided bombs that work like this are still around, as it's a simple and reliable system that just works).
Click to expand...
Thank you very much :D
 
J

Jeremy Harris

Senior Member
hippy said:
AIUI this is a 'drone locating an item in a room' challenge.

The ultimate application is to locate a radioactive source but the proof of concept will use RF rather than radiation.

There will be one RF transmitter attached to the item and four RF receivers on the drone, each with directional antenna. Received signal strength will be used to figure out where the item is.

That sounds simple enough, but so do many one line project specs written on the back of napkins.
Click to expand...
I misunderstood, thought there were multiple transmitters, not just one.

I think that IR, suitably modulated to remove any steady-state interference, would be easier than using RF. It's dead easy to make 90 deg horizontal field of view IR sensors, with baffles, and once that's done the "find the transmitter" bit is pretty straightforward, just move in the direction of the sensor with the strongest signal. With 8 sensors, with a 90 deg horizontal and 90 deg vertical FOV things get easier in terms of locating the IR transmitter in 3D.
 
hippy

hippy

Technical Support
Staff member
IR would have its advantage but I don't know if that would take things too far away from what this proof of concept is meant to demonstrate or prove, though I am not sure what that is.
 
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manuka

Senior Member
... though I am not sure what that is.
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If you're not sure then imagine -sigh- how we feel!

The YouTube video above was produced at a New Zealand high school near Auckland. It's quite possible my PICAXE/Dorji work at the time (2012) stimulated this fellow Kiwi. Refer hence my similar Instructable.

I agree that indoor RDF (Radio Direction Finding) will be a multipath nightmare. Such "fox hunting" RF tracking methods as Doppler Shift or TDOA (Time Difference of Arrival) can give workarounds, but they suit longer (outdoor) ranges, & circuitry can be complicated. Check this 1990 era 555 timer based TDOA setup, and also past Forum pondering .

Even IR (Infra Red) may have wall/floor/ceiling or reflective window etc bouncing issues. It may be akin to trying to swat mosquitoes,hunting flies with a vacuum cleaner or locating a cell phone lost somewhere in the house! !

EXTRA: News just to hand- LoRa™ (Semtech's Long Range) may suit IoT GPS-free geolocation using
Differential Time of Arrival. Although accuracy looks only modest,the technique suits "battery for life" IoT devices. See here and here.

Stan.
 
R

rossko57

Senior Member
hippy said:
A directional antenna can be used with any RF receiver.
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I think perhaps we should qualify that a little for the OP.

You do need an antenna that matches the particular radio frequency in use - they are not all alike.

Not all ready made RF module designs make it easy to attach any kind of external antenna. The product first proposed here looks like one of those, i.e. it is not practical to use an antenna with that.

If this drone is flying, remember you have a 3-dimensional problem - you'll be looking for azimuth as well as compass direction. Presumably the drone can circle or rotate bodily to search the compass? But searching the vertical would not be physically as easy?
Note also that circling would need some thought about how to interpret a target inside the circle.

You might also need to think about providing the Tx module with an external "omni" aerial, some ready made modules might not be very good at being a non-directional beacon in 3 dimensions. Don't expect miracles for four dollars.


I've got to agree, this is tough stuff and looks to be too ambitious for current skill levels. Can you not start simpler? We've not even touched on other tricky bits - how could you control this drone, how much extra weight can it carry, what is the effect of sticky-out antenna etc.
 
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eggdweather

Senior Member
Luckily drones are not that aerodynamic, so carrying 4 antennas is viable.
2.4 or 5.8GHz is the only viable choice of frequency because then antenna sizes become small.
Operating RF in the near field means that all antennas will receive about the same signal level, even with directional antennas, the only way I know of detecting direction in these circumstances is time and phase difference of arrival as Manuka has already mentioned, that is not a trivial task to engineer in hardware or software.
You can get small 'bug' like devices that can achieve radio direction finding, where they have implemented some form of TDOA, which you may be able to interface to, but overall this is IMO a viable but extremely demanding project to implement and requires a large technical domain knowledge to achieve success.
 
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rossko57

Senior Member
We don't know what the OP means by "drone" - given the unknown end ambition it could be a fixed-wing or blimp.
 
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eggdweather

Senior Member
Most radio amateurs are very adept at RF direction finding, armed with a receiver and directional antenna and a just a signal strength meter, usually the one in the receiver, I have been on so-called foxhunts at UHF and the outcome enables quite good location accuracy to be obtained, usually with 3-4 M of location accuracy. You'd need a map (obviously) and to take readings at three different locations and then plot those relative highest signal strength directions and you what's colloquially called a 'crooked hat' and within that will be the target location, by further refining the process, accuracy is improved. To do that on a drone would require 4 directional antennas and the Picaxe would need to sample received signal strength from each then rotate and move the craft through a known angle (of yaw) and any different location and then repeat and do some trig, so viable, but still a lot of skills required.
 
J

Jeremy Harris

Senior Member
eggdweather said:
Most radio amateurs are very adept at RF direction finding, armed with a receiver and directional antenna and a just a signal strength meter, usually the one in the receiver, I have been on so-called foxhunts at UHF and the outcome enables quite good location accuracy to be obtained, usually with 3-4 M of location accuracy. You'd need a map (obviously) and to take readings at three different locations and then plot those relative highest signal strength directions and you what's colloquially called a 'crooked hat' and within that will be the target location, by further refining the process, accuracy is improved. To do that on a drone would require 4 directional antennas and the Picaxe would need to sample received signal strength from each then rotate and move the craft through a known angle (of yaw) and any different location and then repeat and do some trig, so viable, but still a lot of skills required.
Click to expand...
But this is inside a room that's a few metres square, where there will be multiple reflections from every surface.....................
 
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eggdweather

Senior Member
Thanks, yes I forgot, plus almost certainly the RF will be affected by interaction by people in the Fresnel zones making reliable and repeatable measurements nearly impossible.

To use TDOA and assuming a room size of 5Mx5M and the craft about 5M away from the source of RF, then the processor would need to be able to detect time differences of:
time to travel 5M = 5/3E8 = 0.0166uS
say the antennas were arranged in a quad shape spaced, 1M apart, then
time to travel 6M = 6/3E8 = 0.02uS
So the difference (Time difference of arrival) would be 3.3nS, so the processor would need the resolution to read with a resolution the timing down to very low levels.
As good as it is, the PICAXE cannot achieve TDOA - is my view.

Now add multiple path RF from reflections and this is more evidence that this is not a viable project for most people.
 
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